"Shelf-Life" of Alum 6061 Tubing 1

[pip123]

Is there such a thing as a shelf-life for seamless 6061-T4 tubing? What about 6061-T6?
The diameter of the tubes in question is 2" and less and we store them indoors.
By shelf-life I mean a change in yield strength or hardness over time (6 months to years).

I have been unsuccessful in obtaining information from our tubing supplier.

Thanks in advance for any thoughts.

 

[CoryPad]

I don't know about T4, but T6 is stable at room temperature essentially forever.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[israelkk]

To my best knowledge there is no shelf life for metals or metal alloys. Yield strength or hardness will never change as long as it is not exposed to high enough temperatures that can overage or soften the metal. As long as there is no corrosion that can weaken the tubes or penetrate the wall thickness the tubes can be used.

 

[IFRs]

Aluminum probably won't age harden unless temperatures higher than ambient (but not too high to caus annealing) are involved. I have also run into age hardened steel - old steel that is very hard to drill through, but I am less sure of the metallurgy.

6061-T4 is solution heat-treated
6061-T6 is T4 + artificial aging

More?

Alloys in the 2xxx, 6xxx and 7xxx groups can be strengthened by a heat treatment process. The aluminum is heat treated by carrying out a solution treatment process, in which the metal is heated to an elevated temperature followed by rapid cooling, then a precipitation hardening process (or "aging" process). The tempers are designated by -T followed by a digit. Some common -T tempers are as follows:

-T3

Solution heat-treated, cold worked and naturally aged: Applies to products that are cold-worked to improve strength after solution heat-treatment, or which the effect of flattening or straightening is recognized in mechanical property limits

-T4

Solution heat-treated and naturally aged: Applies to products that are allowed to age harden at room temperature following a solution treatment.

-T6

Solution heat-treated and artificially aged: Applies to products that are reheated to a low temperature following a solution treatment. This allows the metal to achieve its highest heat-treated strength level.

 

[49078]

6061 T4 is an alloy that will naturally age even at room temperature. The properties may change over time, but I don't know to what extent. T6 is precipitate hardened and should be stable enough that the properties stay unchanged over time at room temperature.

 

[CoryPad]

I consulted the ASM Handbook. Even at 100 [°]C, the yield strength changes less than 5% over one year.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[pip123]

Thanks to all for the replies.

CoryPad:
Can you please list your ASM reference?
I'll use it to document the information.

Thanks again,
Ron

 

[CoryPad]

ASM Handbook Volume 4: Heat Treating, section Heat Treating of Aluminum Alloys, subsection Strengthening by Heat Treatment.

http://www.asminternational.org/Tem...=Ecommerce/ProductDisplay.cfm&Productid=10438

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[NickE]

"To my best knowledge there is no shelf life for metals or metal alloys. Yield strength or hardness will never change as long as it is not exposed to high enough temperatures that can overage or soften the metal."

Actually the low carbon, no alloy steels will age at room temperature. This is a result of solution amounts of nitrogen and carbon in the steel. (IE really soft 1004/1006 only will have its good forming properties for ~6mths at room temp). The newer IF (interstitial free) steels do not do this and are referred to as stabilized grades.

If the Deep Drawing Quality steel sits too long in the warehouse then it will develop stretcher strains (luder lines) in the steel when formed.

One way to prevent this is to temper roll or strech level the material. This is done by appling ~.5% strain to the steel.

 

[strokersix]

NickE,

What material property changes would occur as 1004/1006 ages? Magnitude and how quickly?

 

[NickE]

Ive seen DDQ steels lose r-value (not r-bar) and elongation in the standard tensile test. Yield goes up a bit also. You can also see aging in the Olsen test. Luder Lines or Strecher strains are more cosmetic than mechanical.

For highly drawable and formable grades the Mill wont generally consider the mechanical certs good past 6months.

For parts right near the forming limit this aging can mean the difference btw. a good part and bad part.

(note the above applies to common drawable grades of steel. I have no knowledge of aging in other grades.)